1. Field of the Invention
This invention relates to a side-lighting light guide plate and a side-lighting backlight module, specifically to a local dimming side-lighting light guide plate and a local dimming side-lighting backlight module.
2. Description of the Prior Art
Display panels and flat displays using the display panels are now the mainstream of the display devices. In addition, the liquid crystal displays are the mainstream of the flat displays and are extensively used in various types of electronic products such as display screens, home televisions, monitors for personal computers and laptop computers, display screens of mobile phones and digital cameras.
The backlight module is one of the key components of the conventional liquid display panels. The liquid crystal itself does not generate light and a backlight module is used to provide adequate and evenly distributed luminance for the liquid crystal display panel to display images properly. The conventional backlight module uses only a single light guide plate to guide the light generated by the light sources, wherein the luminance at different portions of the light guide plate is substantially equal. However, in order to improve the visual effect of the displayed images, the backlight module should be able to present luminance of different magnitudes at different portions of the light guide plate.
As for the conventional direct-lighting backlight module, the light sources are disposed directly below the display panel. In this way, the direct-lighting backlight module only needs to drive the light source below the portion of the light guide plate needing luminance and close other light sources to achieve the desired contrast of the display image. However, for the side-lighting backlight module, light generated by the light sources enters the light guide plate and then disperses as the moving distance increases. In other words, the light guide plate cannot limit the light in one particular region. In this way, the conventional side-lighting backlight module cannot achieve the desired contrast by driving and closing the light sources like the conventional direct-lighting backlight module.
FIG. 1 is an exploded view of a conventional side-lighting backlight module 10. As FIG. 1 shows, the side-lighting backlight module 10 includes a reflector 11, a light guide plate 40, a light source set 50, wherein the light source set 50 is disposed at two sides of the light guide plate 40.
In the embodiment illustrated in FIG. 1, the light source set 50 includes a plurality of light sources 51, wherein the light sources 51 can be light emitting diodes. Similarly, different portions of the light guide plate 40 are defined by the light sources 51 as a plurality of light areas, wherein each light area of the light guide plate 40 corresponds to one or more different light sources 51. The light source 51 thus can be selectively driven to provide the corresponding light area with the required luminance.
As FIG. 1 shows, an upper structure layer 41 is disposed on the surface of the light guide plate 40. The upper structure layer 41 includes a plurality of prisms 41a, wherein the prism 41a extends from one side of the light guide plate 40 near the light source set 50 toward the opposite side near another light source set 50. The extending direction of the prism 41a is parallel with the travelling direction of the light emitted by the light source set 50. In this way, lights generated by the light source set 50 travel in the extending direction of the prism 41a toward the opposite sides of the light guide plate 40 and will not greatly disperse in other directions. This helps with the control of luminance in light areas. For this reason, the extending directions of the prisms 41a are substantially parallel, but are not limited thereto; in different embodiments, an angle can be included between the extending direction of the prisms 41a and the extending direction of the light.
A microstructure layer is disposed at the bottom of each light area of the light guide plate 40 for destroying the total reflections of the lights so that those lights can eventually emit from the surface of the light guide plate 40 that is disposed with the upper structure layer 41.
However, the light guide plate 40 is integrally formed into one piece by same material. There is thus no other structure or material for blocking light generated by adjacent light sources 51. In this way, only a portion of the light generated by the light source set 50 will travel in a direction parallel with the extending direction of the prisms 41a. Other portions of the light will disperse in different directions and is eventually affected by the microstructure layer and then emit from the surface of the light guide plate 40 corresponding to other light areas. In other words, the light guide plate 40 cannot limit the light generated by a particular light source 51 within a specified region and therefore the conventional side-lighting backlight module 10 cannot improve the contrast by selectively driving light sources 51.
The conventional side-lighting backlight module 10 mentioned above can still use a V-shaped structure layer 41 and the microstructure layer corresponding to the light areas to achieve local dimming and improve the contrast of the displayed images. However, this design still cannot effectively eliminate the problem of light leakage to the adjacent light areas mentioned above.